The impact of large structural brain changes in chronic stroke patients on the electric field caused by transcranial brain stimulation
The impact of large structural brain changes in chronic stroke patients on the electric field caused by transcranial brain stimulation
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DOI：
10.1016/j.nicl.2017.04.014
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发表时间：
2017-01-01
影响因子：
4.2
通讯作者：
Thielscher, Axel
中科院分区：
文献类型：
--
作者：
Minjoli, Sena;Saturnino, Guilherme B.;Thielscher, Axel
经颅磁刺激（TMS）和经颅直流电刺激（TDCS）是两种类型的无创经颅脑刺激（TBS）。它们是中风研究的有用工具，并可能成为功能恢复的潜在辅助疗法。然而，中风往往会导致大的脑损伤，这通常伴随着继发性脑室扩大和萎缩。这些结构改变实质上改变了头部内的电导率分布，这可能对两种脑刺激方法都具有潜在的重要影响。因此，我们的目的是表征这两种TBS方法产生的电场的空间分布上的这些变化的影响。除了确认TBS在存在大的卒中相关结构变化的情况下的安全性外，我们的目的是澄清靶向刺激是否仍然可行。使用两名患者的MR图像创建了包含右侧顶叶皮质中的大皮质和皮质下卒中病变的真实头部模型。对于TMS，使用有限元法模拟了双线圈的电场。测试了线圈位置相对于病变的系统变化。对于TDCS，有限元法被用来模拟一个标准的方法与两个电极垫，和一个电极的位置是系统地变化。对于TMS和TDCS，损伤在皮层中引起电场"热点"。然而，这些最大值并不比健康对照中观察到的那些显著更强。经颅磁刺激诱发的电场模式基本上不受病变的影响。然而，TDCS产生的平均场强大幅下降。两种头部模型都发生了这种效应，甚至当两个电极远离病变时也是如此，这是由于通过病变和扩大的心室分流的电流增加所致。从与健康对照相比相似的峰值场强判断，两种TBS方法在具有大脑病变的患者中是安全的（然而，在实践中，必须考虑其他因素，例如潜在降低的脑损伤诱导阈值）。通过TMS进行聚焦刺激似乎是可能的，但标准tDCS方案似乎不如健康受试者有效，这强烈表明在该人群中进行tDCS研究可能受益于基于实际现场计算的个性化治疗计划。
Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (TDCS) are two types of non-invasive transcranial brain stimulation (TBS). They are useful tools for stroke research and may be potential adjunct therapies for functional recovery. However, stroke often causes large cerebral lesions, which are commonly accompanied by a secondary enlargement of the ventricles and atrophy. These structural alterations substantially change the conductivity distribution inside the head, which may have potentially important consequences for both brain stimulation methods. We therefore aimed to characterize the impact of these changes on the spatial distribution of the electric field generated by both TBS methods. In addition to confirming the safety of TBS in the presence of large stroke-related structural changes, our aim was to clarify whether targeted stimulation is still possible. Realistic head models containing large cortical and subcortical stroke lesions in the right parietal cortex were created using MR images of two patients. For TMS, the electric field of a double coil was simulated using the finite-element method. Systematic variations of the coil position relative to the lesion were tested. For TDCS, the finite-element method was used to simulate a standard approach with two electrode pads, and the position of one electrode was systematically varied. For both TMS and TDCS, the lesion caused electric field " hot spots" in the cortex. However, these maxima were not substantially stronger than those seen in a healthy control. The electric field pattern induced by TMS was not substantially changed by the lesions. However, the average field strength generated by TDCS was substantially decreased. This effect occurred for both head models and even when both electrodes were distant to the lesion, caused by increased current shunting through the lesion and enlarged ventricles. Judging from the similar peak field strengths compared to the healthy control, both TBS methods are safe in patients with large brain lesions (in practice, however, additional factors such as potentially lowered thresholds for seizure-induction have to be considered). Focused stimulation by TMS seems to be possible, but standard tDCS protocols appear to be less efficient than they are in healthy subjects, strongly suggesting that tDCS studies in this population might benefit from individualized treatment planning based on realistic field calculations.